Charge Transport in Anisotropic Lamellar Structure of Conjugated Polymers

Abstract

The π-π interactions in conjugated polymers make the polymer chain folded into lamellas, which stack up to form a nanofiber. The chain folding interrupts conjugation and, consequently, limits the on-chain motion of charge carriers to the range of nanofiber width only. Charge carriers, usually positively charged holes, are transported in the polymer bulk by means of hopping among the conjugated chain segments. In this paper, we put forward a new theoretical model of the charge transport combining the quantum and semiempirical approaches, and elucidate particularities of the charge transport in this kind of materials. While the charge carrier states on a single conjugated chain segments are described within quantum chemistry by a tight-binding model, the inter-chain charge carrier hopping is treated within the semi-classical Marcus theory taking into account a charge carrier thermalization between subsequent hops. Numerical calculations performed on poly(3-hexylthiophene) as an example of conjugated polymer with lamellar structure showed that the presented model can describe the dependence of the hole mobility on the electric field for various mutual orientations of the electric field and the lamellas. This is important for theoretical simulations of the performance of real organic electronic devices, namely electrical characteristics of the organic field-effect transistors.